Revue canadienne de biologie experimentale最新文献

Membrane potential and photoresponse of rods in the isolated toad retina was recorded while changing the ionic composition of the extracellular medium. In the presence of 10 mM external Cs+ the bright flash response consisted of an initial fast component of about 35 mV followed by a much slower component as large as 50 mV. The slow component of the photoresponse was blocked by micromolar amounts of both ouabain and strophanthidin. The effects induced by the latter were almost completely irreversible. The effects induced by changing the external concentrations of Na+, K+ and Ca2+ were analysed assuming that the amplitude of the slow component of voltage photoresponse reflects the activity of Na+--K+ pump. It is shown that external Na+, K+ and Ca2+ have the same effect on the amplitude of the slow component as on the Na+-K+ pump activity of other tissues.

Throughout the history of the biological disciplines from the 18th to the 20th centuries, there has been a succession of predominating fields of interest: morphology, physiology, genetics, biochemistry, ecology and ethology, while statistics, biometry and computer sciences were developing as powerful means of imposing rigor on research. In all sciences, there is a fundamental empiricism which has often been criticized as prescientific. However, it is unavoidable, especially in biology owing to the unusual wealth and complexity of the facts to be reported. Explaining in the natural sciences first requires the discovery of relationships between facts. Biological explanation has many levels. One of the main avenues leading to true explanation is the multidisciplinary approach, which is in reality an attempt at synthesis. Another characteristic of biological work is the equilibrium between pragmatism and idealism, usually expressed as a balance between application and theory. Both modalities are necessary because of their complementarity. The emergence of ecology demonstrates this duality in the recent past. The equilibrium between theory and application should be decided by the biologists themselves, not by the funding public agencies, although competent administrators are necessary for the welfare of researchers. Applied and theoretical research should be kept separate to a large extent, even though they remain interdependent. In biology, theoretical work has suffered considerable neglect as compared to the situation in physics and chemistry. Biology has few explanatory theories and the few it possesses have often been put forward by physicists in the field of biophysics.(ABSTRACT TRUNCATED AT 250 WORDS)

The purpose of the present investigation was to examine, in the light of recent histological findings, whether irradiation and colloidal carbon can have a lymphocyte depopulating effect on preferentially particular structures of the rat lymph nodes. Normal eight-week-old Sprague-Dawley rats received a 500 R whole body irradiation or a subcutaneous injection of 0.02 ml of India ink. The animals were then sacrificed at various time-intervals. The histological analysis of the irradiated and draining nodes revealed that both treatments almost completely eliminated small lymphocytes from the affected nodal structures, except in the center of the deep cortex units. The affected structures had been predominantly populated by recirculating lymphocytes.Thus, the treatment had a rather preferential depleting effect on a node population of recirculating lymphocytes. This finding provides another possible explanation for the carbon-induced augmentation of a GVH reaction in nodes. This augmentation had previously been attributed to a stimulation by the carbon of host macrophages, which would mediate the proliferation of antigen-reactive donor cells. From our present findings, it appears that carbon, like irradiation, could act by depleting a node of recirculating lymphocytes, thereby weakening its immunological potential against the inoculated lymphocytes.

Chick embryos were cultured in hemispheric dishes containing 25 ml fresh albumen. The addition of albumen, known to the relatively poor in free calcium, increased the deficit of calcium regularly observed in embryos cultured with other methods. In spite of this, the embryos survived and differentiated adequately for prolonged periods of time. Most of the cultured embryos presented malformations of the long bones of the limbs consisting of bowing and exuberant growth of bone trabeculae in the concavity of the bend. Block staining with alizarin showed that bones were undermineralized at the time in which bending occurred. Leg muscles differentiated adequately as judged from their electron microscopical observation. It is concluded that the malformations result from the action of normal muscles on undermineralized bones. The growth of bone trabeculae at the concavity of the bend probably results from the piezoelectrical stimulus produced by the bending of the bones. The concentrations of both the ionized and bound fractions of blood calcium were significantly reduced in the cultures. The system appears to constitute an adequate model for further explorations on the effects of prolonged hypocalcemia on the differentiation of different tissues and organs.

The structures involved in ocular accommodation were studied with scanning electron microscopy in 5-day old chicken. Particular attention was paid to the ciliary muscle that was found to be subdivided into an anterior and a posterior portion. Since the anterior portion inserted on the wall of canal of Schlemm, we postulate that it could somehow control the flow of aqueous humour. According to its insertions, the posterior muscle could stretch the choroid coat. Thus, changes in the refractive power of the eye would be brought about by an indirect mechanism.

The photopic spectral sensitivity of the rainbow trout, Salmo gairdneri, was determined using a two choice appetitive training method. The resulting curve had three maxima at around 391-473, 490-573 and 650-669 nm. Maximum sensitivity was reached with short wavelength stimuli. Thresholds for white light were also obtained. The results show that the rainbow trout has an action spectrum that is similar to that of other fresh water teleosts in similar circumstances, and that it most likely has the ability to distinguish monochromatic stimuli on the basis of wavelength. Using thresholds to white light and typical freshwater visual pigments, the form of the spectral sensitivity curve was found to be best fitted by independent receptor action at the short wavelengths and by inhibitory interaction between the green and red receptors at the longer wavelengths.

The addition of a concentrated, calcium-equilibrated TRIS buffer to serum samples, facilitated the determination of the level of ionized calcium (iCa) without interference of pH changes due to CO2 loss. Determinations were carried on sera from chick embryos of various ages and compared with values obtained in the sera from young chicks. It was found that iCa levels in the embryos were significantly higher than those obtained in young chicks, the decrease beginning during the first day after hatching. These results help in the clarification of the mechanism(s) inducing the high calcitonin levels observed in the embryonic serum by previous authors.

After concentration with PEG-6000 and purification on a metrizamide gradient, the Lymphocystis Disease Virus (LDV) can be shown as a particle with a chemical composition of 1,6% DNA, 42,3% protein and 17,1% lipid, most of them being phospholipids. Sugars might constitute a major portion of the 39% unidentified components.

The in vivo effect of either poly-L-Lysine, poly-L-Glutamic acid or poly-L-Glycine on mouse spleen cell populations was investigated. The membrane fluorescence changes of activated splenic lymphocytes were studied. Experiments were performed with the hydrophobic fluorescent probe: 1-anilino-8-naphthalene sulphonate (ANS). Kinetic studies further indicated that the course of fluorescence changes may vary considerably depending upon homopolymers. These fluorescence intensity changes would be in direct or inverse relation to the electrokinetic surface potential changes of activated lymphocytes, as assessed by the electrophoretic mobility analysis. It could be concluded that the relation (direct or inverse) between ANS fluorescence and electrokinetic potential depends upon the net electrical charge of the homopolymer used. In further experiments, the determination of the net electrical charge of some tumour antigens could be considered without hard purifications.